X-ray technology has been applied to a wide range of medical, industrial, and scientific problems. In part, this is a consequence of the varied properties of X rays, including differential absorption, quantitative measurement of absorption, diffraction by crystals, fluorescence of characteristic radiation, and biological effects produced by X rays. One of the earliest applications of X-ray technology was to medicine, being used in both diagnosis and therapy. Diagnostics include the detection of bone fractures, foreign objects in the body, dental cavities, and diseased conditions such as cancer. In therapeutic treatment, X rays are used to stop the spread of malignant tumors, and in conjunction with other non-invasive procedures. X-ray technology has also been used in a number of industrial applications. For example, X-ray radiographs have been used to detect flaws in castings that are inaccessible to direct observation and to measure the thickness of materials.
The study of X rays has also played a vital role in theoretical physics, especially in the development of quantum mechanics. As a research tool, X rays enabled physicists to confirm experimentally the theories of crystallography. By using X-ray diffraction methods, crystalline substances may be identified and their structure determined. Virtually all present-day knowledge in this field was either discovered or verified by X-ray analysis. X-ray diffraction methods can also be applied to powdered substances that are not crystalline but that display some regularity of molecular structure. By means of such methods, chemical compounds can be identified and the size of ultramicroscopic particles can be established. Chemical elements and their isotopes may be identified by X-ray spectroscopy, which determines the wavelengths of their characteristic line spectra. Several elements were discovered by analysis of X-ray spectra.
A number of recent applications of X rays in research are assuming increasing importance. Microradiography, for instance, produces fine-grain images that can be enlarged considerably. Color radiography is also used to enhance the detail of X-ray photographs; in this process, differences in the absorption of X rays by a specimen are shown as different colors. Extremely detailed and analytical information is provided by the electron microprobe, which uses a sharply defined beam of electrons to generate X rays in an area of specimen as small as 1 micrometer (about 1/25,000 in) square. One limitation on the usefulness of X-ray technology, however, has been the limited ability to provide three-dimensional information of the object being examined. It is difficult to create a stereo image of the structure inside an object from two-dimensional radiographs.
Several complicated systems have been devised to obtain three dimensional information, including transmission X-ray microscopes. X-ray microscopy combines X-ray transmission systems with tomographical reconstruction methods, enabling recreation of three-dimensional information of the internal microstructure. These methods and resulting images can be used to analyze the two- and three-dimensional anatomical structure using a set of flat cross-sectional images. These methods rely on the contrast in the images, which represents a mixed combination of density and compositional information. In some cases, the compositional information can be further separated from the density information. This method, however, requires a large number of different cross-sectional images of an object resulting in increased exposure to potentially harmful radiation. Additionally, the images must be taken with great care in order to provide the correct cross-sections.
Another X-ray imaging device is a Computerized Axial Tomography scanner (also known as a "CAT scanner," or "CT scanner"), which is a medical diagnostic test device that combines the use of X rays with computer technology. A series of X-ray beams from many different angles are used to create cross-sectional images of the patient's body. These images are assembled in a computer into a three-dimensional picture (in the way similar to tomographical reconstructure) that can display organs, bones, and tissues in great detail.
However, these facilities are complicated, expensive and are often not accessible to most researchers and users. What is needed, then, is a system and method for extracting three dimensional information from two-dimensional X-ray images that is relatively simply to use, accessible to both small and large medical and research facilities, while providing limited exposure of a patient or other object to radiation.